symlink vs. directory "conflicts"

Hi,
we recently had a thread here about missing copyright files due to bad
transition from /usr/share/doc/directory to
/usr/share/doc/symlink->other_directory, a lot of bugs were filed and
are getting fixed.
There are also more complicated^Wmessed up cases like sendmail that has
maintainer scripts that try to setup /u/s/doc/sendmail-foo -> sendmail
symlinks while at the same time shipping /u/s/doc/sendmail-foo/README
etc. where several packages are overwriting each other (without dpkg
having a chance to notice this). This is being cleaned up in #681147
So what is the general recommendation about packages that ship files
over symlinked directories? Should this be forbidden because it opens
cans of worms?
foo ships /usr/share/foo/foo.dat
bar ships /usr/share/foobar/bar.dat
/usr/share/foo -> foobar
Whoever gets installed first wins. And if bar decides to change the link
to e.g. /usr/share/foo -> f00bar, things get more funny. And foo loses
its foo.dat.
We should probably analyze the current situation first - how many
possible clashes do we currently have? Therefore we would need
"Contents" files annotated with types (and including directories), so
that we can look for conflicts. And while we do this, we could also look
for directory vs. file conflicts and symlink vs. file conflicts ...
Andreas